1. Field of the Invention
The invention relates to an exercise apparatus, more particularly to an improved magnet-type resistance generator for an exercise apparatus.
2. Description of the Related Art
Exercise apparatuses with magnet-type resistance generators are known in the art. FIGS. 1 and 2 illustrate a conventional exercise bicycle which incorporates a magnet-type resistance generator. The resistance generator includes a magnet unit (B) which pivots frontward and rearward and which is disposed adjacent to a periphery of a flywheel (A) of the exercise bicycle. When the magnet unit (B) pivots frontward, the periphery of the flywheel (A) cuts into a magnetic field that is generated by the magnet unit (B). Referring to FIG. 3 , the magnet unit (B) utilizes several spaced pairs of oppositely polarized permanent magnets (B1) to generate the magnetic field.
A cantilever (C) is disposed on one side of the flywheel (A). A link mechanism (D) mounts pivotally the magnet unit (B) on the cantilever (C). The link mechanism (D) includes a pair of parallel cranks (D1). A shaft sleeve (D2) is provided on each end of each crank (D1). Each shaft sleeve (D2) is formed with an axial through hole (D3). A rocking arm (E) interconnects the upper ends of the cranks (D1). The rocking arm (E) has a rear side which is secured to a side wall of the magnet unit (B), and a front side which is formed with a spaced pair of frontwardly extending shafts (E1). Each of the shafts (E1) extends into the shaft sleeve (D2) on the upper end of the respective crank (D1). Nuts (D4) engage the distal ends of the shafts (El) so as to mount the cranks (D1) pivotally on the rocking arm (E). The cantilever (C) has a front side which is formed with a spaced pair of frontwardly extending shafts (C1). Each of the shafts (C1) extends into the shaft sleeve (D2) on the lower end of the respective crank (D1). Nuts (D4) engage the distal ends of the shafts (C1) so as to mount the cranks (D1) pivotally on the cantilever (C). A push piece (D5) is secured on the upper end of one of the cranks (D1). The push piece (D5) is formed with a vertically extending notch (D6). The distal end of a bent pull shaft (F1) is received in the notch (D6) and is movable upwardly and downwardly therein. The other end of the pull shaft (F1) is connected to a slide piece (F2) of a bolt unit (F). The slide piece (F2) is mounted threadedly on a guide bolt (F4) that is driven rotatably by a motor (F3). A gear (F5) is secured on a distal end of the guide bolt (F4). The gear (F5) meshes with another gear (F51) which is driven rotatably by the motor (F3). The upper end of the slide piece (F2) is formed with an upwardly extending rod (F21). A slide potentiometer (F6) is disposed parallel to the guide bolt (F4). The rod (F21) moves a slider (not shown) of the slide potentiometer (F6) frontward and rearward. Referring to FIG. 4, the slide potentiometer (F6) is connected electrically to a voltage sensor. The voltage sensor includes a position sensor (G11) and a position control (G12) and is connected electrically to a computer (G2). The computer (G2) is connected to a motor control unit (G) which, in turn, is connected to the motor (F3) so as to control the rotation of the latter.
Referring once more to FIGS. 1 to 4, an instrument control unit (H) is operated so as to adjust the resistance that is to be provided by the bicycle exerciser to the desired level. The computer (G2), which is disposed in the instrument control unit (H), commands the motor control unit (G) to activate the motor (F3) and rotate the gears (F5, F51) in order to rotate correspondingly the guide bolt (F4). The slide piece (F2) moves forward or rearward in accordance with the direction of rotation of the motor (F3) and moves the pull shaft (F1) therewith. Movement of the pull shaft (F1) causes forward or rearward pivoting movement of the link mechanism (D). At the same time, the rod (F21) moves the slider of the slide potentiometer (F6) frontward or rearward, thereby adjusting the resistance output of the latter. The position sensor (G11) and the position control (G12) generate a control signal to the computer (G2) in accordance with the instantaneous resistance output of the slide potentiometer (F6). The computer (G2) continues to command the motor control unit (G) to activate the motor (F3) until the desired resistance to the rotation of the flywheel (A) is attained. When the link mechanism (D) pivots forward, the periphery of the flywheel (A) cuts deeper into the magnetic field that is generated by the magnet unit (B), thereby resulting in a larger resistance to the rotation of the flywheel (A). When the link mechanism (D) pivots rearward, a smaller portion of the periphery of the flywheel (A) cuts into the magnetic field that is generated by the magnet unit (B), thereby resulting in a smaller resistance to the rotation of the flywheel (A). When the flywheel (A) ceases to cut into the magnetic field that is generated by the magnet unit (B), no resistance to the rotation of the flywheel (A) is produced.
From the foregoing, it has been shown that in order to convert the rotation of the motor (F3) into pivoting movement of the link mechanism (D) and the magnet unit (B), movement of several components, such as the gears (F5, F51), the guide bolt (F4), the slide piece (F2), and the pull shaft (F1), is required. This results in a relatively large tolerance. The following are some of the drawbacks of the above described resistance generator:
1. Referring once more to FIGS. 1 and 3, the magnet unit (B) confines a groove (B2) between the spaced pairs of oppositely polarized permanent magnets (B1). The periphery of the flywheel (A) extends into the groove (B2) such that the permanent magnets (B1) are disposed on two sides thereof. In order for the flywheel (A) to cut equally through the magnetic lines of the permanent magnets (B1), the flywheel (A) must be disposed at the center of the groove (B2). However, because of the presence of the relatively large tolerance, the flywheel (A) usually does not cut equally through the magnetic lines. This often results in an unstable resistance to the rotation of the flywheel (A). The exercise apparatus thus becomes uncomfortable to use and can result in uneven muscle development.
2. Proper installation and adjustment of the magnet unit (B) is difficult to achieve. When the magnet unit (B) accidentally bumps into an object, the flywheel (A) is easily displaced from its proper position.
3. Note that the instrument control unit (H) is operable in order to set the desired calorie loss and to compute the actual calorie loss. To compute the calorie loss, two factors are required: the rotational speed of the flywheel (A) in revolutions per minute, and the resistance offered by the resistance generator to the rotation of the flywheel (A). As mentioned hereinbefore, the resistance to the rotation of the flywheel (A) is usually uneven. Thus, the computed calorie loss is usually inaccurate.